Working Principle of Transformer

Working Principle of Transformer

A Transformer is a static device which transfers electrical power from one circuit to another circuit without change in frequency. During this period frequency will be same in both circuits. But during this process current and voltage will be different according to the type of transformer. Transformer works on the principle of mutual induction or faraday’s law of electromagnetic induction.

Working Principle of Transformer

Faraday’s Law of Electromagnetic Induction

According to faraday’s law of electromagnetic induction:

“The rate of change in flux with respect to time is directly proportional to the induced EMF in a coil or conductor”

According to this law if flux changing rate increases with respect to time then induced EMF will also increases in conductor.

And if flux changing rate decreases with respect to time then induced EMF will also decreases. In this principle the flux should be variable.

Basic Theory of Transformer

Transformer is a static device which means it does not have any rotation part, it’s all parts are static. A simple transformer has two inductive coils which are electrically separated but magnetically linked to each other by an iron core. This iron core provides a path of law reluctance which causes mutual induction between two coils.

It has two inductive windings, first one is primary winding and second one is secondary winding.

Primary Winding

We give alternate supply to primary winding using alternate electric source.

Alternate flux is produced in this winding and this alternate flux is linked with secondary winding by an iron core path. If secondary winding circuit is closed, current will flow in this circuit according to faraday’s law.

Secondary Winding

We take output supply from secondary winding. An EMF is induced in secondary winding due to primary winding because primary winding is magnetically linked with secondary winding. The output voltage depends on the number of turns in secondary winding.

Tranformer - Primary Winding and Secondary Winding

More about Transformer

Transformer rating is always taken in KVA (Kilo Volt Ampere) not KW (Kilo Watt) because In Transformer rating does not include power factor. If we also include power factor then we take rating in KW. It means

KW = KVA x Power Factor

Transformer depends on load power factor, so we take its rating in KVA.

KVA = V x I
KW = V x I x Power Factor

Where V = Voltage and I = Current


If primary voltage is greater than secondary voltage then transformer is called as step down transformer and if primary voltage is less than secondary voltage then the transformer is step up transformer.

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